1. Field of the Invention
The present invention generally relates to a plasma excitation module, and more particularly, to an inductively coupled plasma excitation module (ICP excitation module).
2. Description of Related Art
Plasma is an ionized gas, which contains ions or electrons and free radicals. The plasma gets broad applications today. As one of the various applications thereof, the plasma processing commonly refers to convert gas into plasma, so as to deposit a plasma gas onto a substrate or to use a plasma gas for cleaning, coating, sputtering, plasma chemical vapour deposition (plasma CVD), ion implanting, ashing or etching. When a common plasma processing equipment is running, a powerful electric field is established between two electrodes, so that a process gas fed between the two electrodes is ionized or dissociated to produce the plasma.
In terms of the development situation of displays today, the main targets are focused on the research and application development of large-scaled displays and flexible displays, wherein the most important issue in the commercial course thereof is about the high uniformity of a large-scaled substrate. The capacitively coupled plasma (CCP), as the conventional technique, has been limited to a low plasma density, so that the processing rate of the plasma equipment fails to be effectively increased. As an alternative, the ICP becomes a technique with highly-potential perspective. Due to the high plasma density produced by the ICP, the ICP is also termed as a high-density plasma source, which features employing a plurality of inductively coupled coils for producing plasma. However, the ICP for a large-scaled substrate encounters following problems: (1) a standing wave effect occurs due to the excessive length of the coils, which reduce the efficiency of transmitting energy; (2) the plasma uniformity is hard to be adjusted, particularly at the edge of the coil, in a large-scaled design, and thereby the ununiformity easily makes a great impact on a plasma film deposition or on a plasma etching process.
To solve the above-mentioned problems, in a patent of TW 00449107, it is proposed that the coils are embedded in a dielectric layer, wherein the dielectric layer is disposed in a chamber and located opposite to a substrate chuck. By adjusting the figure of the dielectric layer, the coupling intensity of electric field is desirably changed. However, the scheme provided by the patent requires sintering an appropriate dielectric material to install the coils. In addition, an additional cooling device is required to dissipate the heat of the coils embedded in the dielectric material, which results in a high cost. Since the coils are embedded in the dielectric layer, an equipment adjustment during the testing is quite inconvenient. In terms of the fabrication process of a large-scaled substrate, it is difficult to sinter a large-scaled dielectric layer or to embed the coils.
U.S. Pat. No. 6,868,800 proposes another scheme where the coils have a specific geometry figure, i.e., a symmetric structure including a plurality of major and minor branches. Although the scheme is able to avoid the standing wave effect caused by excessive length of the coils, but the complexity of the coil geometry figure requires a highly increased processing accuracy which results in the fabrication difficulty and the high production cost. In addition, the gas-supplying system is a single side gas-feeding device, which is suitable only for a low atmospheric pressure situation where a diffused state of gas molecules can be easily realized and the plasma density is accordingly more uniform.
U.S. Pat. No. 7,079,085 proposes a new design of the coils in a way of parallel connection and interlaced disposition to each other, where the plasma uniformity is increased by employing two complementary coils. As a matter of fact, the coil is double-loops coil including two winded wires, and every coil is adjacent and parallel to one another. The single-loop coil herein has a power end and a ground end, wherein the power end and the ground end are adjacently disposed. Since two coils build a structure of parallel connection, so that a less general impedance of the coils is obtained. It should be noted that since the adjacent two coils are parallel and interlaced to each other every a distance length and the current flowing directions in the two coils are opposite to each other, a current complementary function is expected, which is advantageous in balancing the distribution of the electric field. The scheme of said coils rests in complexity of fabricating the coils for large-scaled applications and inconvenience of installation thereof.